The present invention relates to a device for filling an anatomical defect. In particular, the device of the present invention is formed of a member which includes a shape memory alloy.
In various body tissues, defects may occur either congenitally or as a result of operative procedures. Such defects may include abnormal openings, for example, in the cardiovascular system including the heart. Procedures have been developed to introduce devices for closing such abnormal openings. Embolization, the therapeutic introduction of a substance into a vessel in order to occlude it, is a treatment used in cases such as patent ductus arteriosus (PDA), major aortopulmonary collateral arteries, pulmonary arteriovenous malformations, venovenous collaterals following venous re-routing operations, occlusion of Blalock-Taussig (BT) shunts, and occlusion of coronary arteriovenous (AV) fistulas.
For example, a PDA is a congenital defect, and thus is present at and exists from the time of birth. In this abnormality, a persistent embryonic vessel connects the pulmonary artery and the aorta, and intervention is usually required to effect closure. A cardiologist may employ a variety of coils for this purpose, the coils being delivered through a catheter and subsequently placed in the opening to permit proper physiological functioning. In some cases, several coils may be used to occlude the opening.
Another abnormality is an atrial septal defect (ASD), which is a defect in the wall of the heart, known as the septum, that separates the right atrium and left atrium. Such as hole in the septum often requires an invasive procedure for closure of the defect. Similarly, intervention is often required in the case of a ventricular septal defect (VSD), a hole in the wall separating the right and left ventricles.
The use of coils in the intracranial region of the brain for embolizing aneurysms or fistulas is also generally accepted.
Each one of the aforementioned exemplary closure applications requires a specially designed coil which may be introduced into the particular anatomical location. For example, the geometry of the lumen in instances of PDA often requires complicated positioning of the coil for proper functioning. Additionally, an initially indeterminate number of coils may be required to close a given defect, as the decision to deliver multiple coils to a particular defect site is governed by the success of any preceding delivery.
A variety of devices and materials have been used to occlude such abnormal channels. For example, U.S. Pat. No. 4,994,069 to Ritchart et al., the contents of which are herein incorporated by reference, discloses vaso-occulusion wire formed of platinum, tungsten, or gold thread. The wire is advanced through a catheter, and upon release from the catheter into a vessel, it assumes a randomly coiled shape. Although the wire of this development is described as having memory, the type of memory property of these materials is not that of a shape memory material having transition temperatures for various material states.
Additionally, U.S. Pat. No. 5,192,301 to Kamiyama et al., discloses a closing plug for closing a defect in a somatic wall. The plug is formed of a polymer such as polynorbornene, styrene-butadiene coploymer, polyurethane, or transpolyisoprene. Although these polymers are described as xe2x80x9cshape memoryxe2x80x9d polymers, they are unlike metallic materials displaying shape memory behavior. Many polymers display a glass-transition temperature (Tg) which represents a sharp change that occurs from a hard and glassy state to a rubbery, soft, or flexible thermoplastic state. If deformed by a load at a temperature below its Tg, a so-called xe2x80x9cshape memoryxe2x80x9d polymer may retain the deformation until heated above the Tg, at which point the deformation and the original shape are recoverable. This characteristic of some polymers is often described as xe2x80x9celastic memoryxe2x80x9d.
A variety of other spring coil configurations have been used, although stainless steel and platinum have emerged as the most common materials. U.S. Pat. No. 5,649,949 to Wallace et al., discloses vosoocclusive coils formed from platinum, gold, rhodium, rhenium, palladium, tungsten, and alloys thereof. Wires formed of composites of these metals and polymers are also disclosed. These materials are inappropriate for the present development because they do not have the shape memory properties of materials such as nitinol. Among the several superior properties of nitinol when compared to stainless steel, the most important include strong physiological compatibility, a substantially lower modulus of elasticity, and a much greater tolerance to strain before the onset of permanent, plastic deformation. In fact, nitinol may have an elasticity an order of magnitude greater than that of stainless steel.
U.S. Pat. No. 5,645,558 to Horton discloses an occlusive device formed of super-elastic alloys, such as nitinol. The device is spherical in shape. U.S. Pat. No. 5,382,259 to Phelps et al. further discloses the use of nitinol shape memory wire to form coils. Fibers are also woven to the coils. These coils do not have the shape of the present development.
Various other coil configurations have been proposed. For example, as disclosed in U.S. Pat. No. 6,117,157 to Tekulve, a helically shaped embolization coil includes bent ends. In addition, U.S. Pat. No. 6,126,672 to Berryman et al. discloses a coil for occluding an intracranial blood vessel. The coil has an anchor in the shape of an xe2x80x9cMxe2x80x9d or xe2x80x9cWxe2x80x9d for contacting the blood vessel. The free legs of the anchor are blunted and reinforced to prevent perforation of the vessel wall.
The success and extent of coil usage may be partially gauged through analysis of the PDA coil registry, the largest database covering use of coils to occlude ducts, which surveys more than 500 cases. Among those included in the database, patients ranged in age from 15 days to 71 years, with a median of 4.2 years. The median PDA size was 2 mm, with a range of less than one to about 7 mm. The immediate complete occlusion rate was 75%, and partial occlusion or any degree of shunt occurred in about 25% of the cases. Failure to implant occurred in 5% of the cases. Coil embolization occurred in 9.7% of the cases involving the pulmonary artery, and in 2.4% of the cases involving the systemic artery.
Analysis of data from the coil registry has revealed that an acute occlusion rate and failure was significantly related to coil size. Shorter studies with longer follow up show a cumulative occlusion rate of 98%. While the registry does not address the overall success rate of closure of PDA-associated ducts greater than 4 mm in size because of the statistical limitations of the data set, the immediate results of procedures directed to large ducts are encouraging. Initial complete occlusion occurred in 84.2%, or 16 of 19 cases. In addition, small residual shunts which closed spontaneously or required a second procedure occurred in 10.5%, or 2 of 19 cases, and failure of the procedure necessitating further surgical intervention to effectuate closure occurred in only 5.5%, or 1 of 19 cases. Coil embolization occurred in 16.5%, or 3 of 19 cases, and left pulmonary artery stenosis occurred in 11%, or 2 of 19 cases. It should be noted, however, that left artery stenosis and failure of the procedure were associated with attempts on neonates and infants. Thus, the effectiveness of coils appears to be unquestionably demonstrated.
The device of the present development may be used in a variety of applications, including but not limited to pediatric cardiology procedures directed at occluding either congenital defects or defects arising during the growth process. As previously discussed, such defects include PDA, ASD, VSD, major aortopulmonary collateral arteries, pulmonary arteriovenous malformations, venovenous collaterals following venous re-routing operations, occlusion of Blalock-Taussig (BT) shunts, and occlusion of coronary arteriovenous (AV) fistulas. The device is also useful in treating patent foramen ovale, a persistent opening in the wall of the heart that failed to close after birth.
The device of the present development is also suitable for use in other non-cardiac, vascular procedures. For example, the device may be used in aneurysmal or fistulous conditions. The shape of the device is chosen based on the shape of the defect. In the case of an aneurysm, the device is placed within the aneurysm as a filler, and may be clipped to ends of the aneurysm to anchor it in place. The device occupies the space of the malformation, with the shape of the device chosen to conform with the shape of the defect. Helical, conical, or spiral device shapes are contemplated, among others.
In addition, the device of the present development may be used specifically for neurovascular applications. The device may be delivered to malformations in the brain, such as aneurysms, tumors, or fistulae.
Moreover, the device of the present development may be use in esophageal, tracheal, or other non-vascular applications. In such instances, the device may be used to fill voids, or extra-anatomic space.
The present invention relates to a device for occluding an anatomical defect in a mammal. The device includes a member formed of a shape memory alloy, the member having a free bottom end and a free top end, a first predetermined unexpanded shape, and a second predetermined expanded shape. The unexpanded shape is substantially linear and the expanded shape is substantially conical, with the expanded shape having a plurality of loops coaxially disposed about a longitudinal axis and progressively decreasing in diameter from one end of the device to the other. At least one of the ends of the member includes a clip having at least two prongs for contacting areas adjacent the anatomical defect.
In one embodiment, the loops form a substantially conical coil having a constant pitch. Alternatively, the loops can form a substantially conical coil having a variable pitch.
The device may be formed of a shape memory nickel-titanium alloy, such as nitinol, and the member may be substantially arcuate in cross-section. At least one of the prongs may additionally include a sharp portion for attaching to an area adjacent the defect. Preferably, the diameter of the plurality of loops is smaller than about 1.5 cm.
The shape memory alloy may display a one-way shape memory effect, or a two-way shape memory effect.
In yet another embodiment, the shape memory alloy displays a superelastic effect at body temperature. Preferably, the shape memory alloy has an austenite finish temperature below body temperature, thereby permitting the device to have superelastic properties at body temperature.
The member may include a plurality of layers. At least one layer may be formed of a passive memory material, and in another embodiment at least two layers may be formed of active memory materials.
In another embodiment, at least one of the layers is a wire formed of a shape memory material, and at least one of the layers is a braid formed of a shape memory material. Preferably, the plurality of layers includes at least two layers braided together or one layer surrounded by a braid.
The device may include at least one crooked section, a substantially conical section, and a substantially cylindrical section disposed between the crooked section and the conical section.
The present invention also relates to a method of occluding an anatomical defect in the vascular tree of a mammal. The method include the steps of: delivering a member formed of a shape memory alloy in a first, substantially straight configuration to an anatomical defect in the body, the member having a temperature below a first transition temperature; and allowing the member to warm above a second transition temperature and form a second, predetermined, coiled configuration having an end with a clip having at least two prongs, wherein the prongs contact areas adjacent the anatomical defect for occlusion of same.
In a preferred embodiment, the second, predetermined, coiled configuration is substantially conical. In another preferred embodiment, the second, predetermined, coiled configuration may include a substantially conical section ending at a free end, at least one crooked section, and a substantially cylindrical section disposed therebetween. Preferably, the second, predetermined, coiled configuration is generally at least one of circular, rectangular, offset coiled, concentric coiled, and combinations thereof.
The present invention further relates to a method of manufacturing a superelastic device for placement inside an anatomical defect, including: providing an inner mandril of a preselected shape for supporting a coil of a wire formed of a shape memory material; winding the wire about the mandril to create a coil conforming to the mandril shape; providing an outer mold to completely surround the coil and mandril and thereby constrain movement of the wire with respect to the mandril; heating the outer mold for a predetermined period of time while the outer mold surrounds the coil and mandril; and allowing the coil to cool.
In addition, the present invention relates to a device for occluding an anatomical defect. The device includes a member formed of a shape memory alloy, the member having a free bottom end and a free top end, a first predetermined unexpanded shape, and a second predetermined expanded shape. The unexpanded shape is sufficiently compact for delivery of the device to the defect. The expanded shape is sufficiently enlarged to occlude the defect by providing a plurality of inner loops and at least one outer loop coaxially disposed about a longitudinal axis, the inner loops progressively decreasing in diameter from a wide end of the device to a narrow end of the device. The at least one outer loop has a diameter greater than the diameter of the inner loops at the narrow end of the device. The device may include at least two prongs for contacting areas adjacent the defect.
The present invention also relates to a method of delivering a device for occluding an anatomical defect. The method includes the steps of: providing a coil having a proximal portion, a transition portion, and a distal portion, and further having an initial length; placing the coil in a movable sheath for delivery to the defect; delivering the movable sheath through the anatomical defect, the anatomical defect having a near side, an inner region, and a far side; withdrawing a portion of the movable sheath from the anatomical defect and allowing the distal portion of the coil to emerge from the sheath; allowing the distal portion of the coil to reach body temperature and expand to a spiral configuration at the far side of the anatomical defect; withdrawing a further portion of the movable sheath from the anatomical defect and allowing the further portion of the coil to emerge from the sheath; and allowing a further portion of the coil to reach body temperature and expand within the anatomical defect.
In a preferred embodiment, the further portion of the coil is the transition portion which expands within the inner region of the anatomical defect. The method may further include the steps of: withdrawing an additional portion of the movable sheath from the anatomical defect and allowing the proximal portion of the coil to emerge from the sheath; and allowing the proximal portion of the coil to reach body temperature and expand to a spiral configuration at the near side of the anatomical defect.